Stone drill



Patented Nov. 26, 1929 UNITED STATESl PATENT OFFICE STONE DRILL Application filed January 23, 1925. Serial No. 4,337.

The present invention relates to a drill for producing holes in` stone and stone-like v materials of all kinds, saidy drill being'of the type which require to be manipulated by a series of blows. The drill is driven into the stone or similar material by means of a hammer, at the saine time being rotated by hand or by means of a suitable holder.

Some of the stone drills of this type hitherto known possess the disadvantage that when being used they are liable to become wedged in the boring being produced, and can then only be rotated with diHculty. The object of the present invention is to overcome this said defect.

According to the invention the cutting edge of the drill is curved outwardly at the leading sides, i. e., at the rear part of each leading side proceeding along the edge of the grooves in lthe shaft. This outward curve of the cutting edge results in the drill after having been driven in to a certain extent automatically releasing itself, becoming loose, and therefore easily capable of being rotated. The effect of this embodiment of the leading sides is still further increased if the trailing sides are ground slightly concave.`

A form of embodiment of the invention'is 3o described by way of example in the following, reference being made to the accompanying drawing.

Fig. 'l is a front elevational view of the drill.

Fig. 2 is an enlarged detail showing the cutting edge.

Fig. 3 is a top plan view of the drill.

Figs. 4, 5 and 6 are sections on lines IV-IV, V-V, VI-VI.

40 The invention is described in connection with a drill 1 having a. holder 2, a chisel-like, curved cutting edge 3, and two grooves 4 in the shaft. The chisel-like cutting edge A3 possesses two alternately disposed leading sides 5 and two trailing sides 6. f

The invention consists in providing the leading sides at the rear part with an outwardly curved elevation 8 running along the edge 7 of the grooves 4: This outwardly curved elevation 8 extends gradually from the outside beyond the centre of the cutting edge '3. If the drill is driven in by means of a hammer the cutting edge 3 at first acts in the usual manner. When, however, the outwardly. curved elevation 8 of the cutting edge comes into contact with the stone or wall, this causes the drill to recoil, the later thus automatically being released or loosened, so that same may be rotated without diiculty, the leading sides 5 operating in the usual, 60 manner.

The eect of .this embodiment of the leading parts 5, 8 is further increased if the trailing parts 6 are ground somewhat concave. Such an inward curvature moreover posc5 sesses the advantage that the material removed from the boring is able to pass without hindrance into the grooves 4. l

What I claim is:

1. A stone drill, comprising a cylindrical, 7o body portion, a curved chisel-like cutting edge at one end of the body portion with leading and trailing sides, oppositely disposed rooves in the body portion,`the leading sidges to the cutting edge being bordered adjacent the grooves with a convex por` tion, -making a slightly greater angle with respect to the axis of said body portion, than the respective sides of said cutting edge, there being no plane with respect to which the ao leading and trailing sides are symmetrical.

2. stone drill comprising a cylindrical body portion, a curved chisel-like cutting edge at one end of the body portion, oppositely disposed grooves in the body portion, convex leading sides to the cutting edge and concave traillng sides to the cutting edge, the leading and trailing sides being unsymmetrical relative to planes including the longitudinal axis of the body portion.

3. A stone drill, comprising a cylindrical body portion, a curved chisel-like cutting edge at one end of the body portion with vleading and trailing sides, oppositelydisposed grooves in the body portion, the leading sides to the cutting edge being bordered adjacent the grooves with a convex portion making a slightly greater angle with respect to the axis of said body portion than the respective sides of said cuttingV edge, there y being no plane with respect to which the leading and trailing sides are symmetrical, the trailing sides being concave.

In testimony whereof I have alixed my signature.

ADALBERT BELA FELDMAR. 

